1. Field of Invention
This invention relates to a fastener tool for the installation of fasteners in a torque-controlled fastening system and, in particular, to a wrench of improved design and construction for such system.
2. Brief Statement of the Prior Art
U.S. Pat. Nos. 4,881,316 and 5,012,704 to George S. Wing, describe a torque-controlled fastening system using a threaded torque collar and a ball driver for the collar. The inventions disclosed in these patents have been commercially adapted under the name NOVA-HEX fastening systems in which six axial lobes are located at equal angular increments on the external surface of the fastener collars. The collars are applied with a wrenching tool that has six rotating, driver balls which are captured in a sleeve retainer. The inwardly facing spherical faces of the driver balls are received in the grooves between the axial lobes of the collars. When the torque applied by the wrenching tool reaches the prescribed limiting torque for the collar and driver, the driver balls roll through the lobes, plowing the material to form a circumferential furrow. The value of the limiting torque depends on the diametric spacing between the faces of opposed balls, which is referred to as the critical diameter.
The aforementioned fastening system provides a number of desirable features such as ease of inspection, as the furrows readily indicate proper application of the fastener collars. Additionally, the torque history of the fastener can be observed by inspection since on reapplication of the fastening collar a wrench is used which has the driver balls at a different axial position, thereby forming a second circumferential furrow through the lobes of the collar. In this manner, up to three applications of a collar can be made, resulting in three axially disposed furrows and a permanent record of the number of installations of the collar.
The wrenching tool disclosed in the '704 patent is prepared by extruding, at extremely high pressure, a soft metal sleeve over the driver balls which are held at precise spacings during the extrusion. The extrusions must then be heat treated at temperatures of about 1725.degree. F. to develop sufficient strength. Unfortunately, the heat treatment causes dimensional distortions, and a majority of the heat treated products must be discarded because of unacceptable variation in their critical diameter.